Field of the Invention
The present invention relates to a flow passage switching unit, which is used in a pneumatic system equipped with an air cylinder.
Description of the Related Art
In an air cylinder, which is widely used as a pneumatic actuator in various types of automated machinery, a piston to which a rod is fixed is moved reciprocally by supply and discharge of compressed air in respective pressure chambers thereof. Additionally, in general, supply and discharge of compressed air with respect to this type of air cylinder is carried out through a switching valve.
Incidentally, in the aforementioned air cylinder, during a working stroke for performing work from among the reciprocating movements of the piston, since an external load is applied to the rod, a large driving force is required. In contrast thereto, during a return stroke when the piston is returned to its original position, since the aforementioned external load is not applied to the rod, the return stroke is completed with a smaller driving force than during the working stroke. The driving force depends on pressure level of the compressed air that is supplied to the pressure chambers. A savings in the amount of air consumption can be realized by reducing the pressure at the time of the return stroke.
Thus, to resolve the above-described problem, an energy-saving valve has been proposed by Japanese Laid-Open Patent Publication No. 2013-024345. The energy-saving valve is equipped with a main valve body in which a valve hole, an air supply port, a first output port, a second output port, and an exhaust port are formed, a single spool slidably inserted in the valve hole, and which connects the first output port and the second output port, respectively, to the air supply port or the exhaust port, a spool driving section that switches the spool from a first position to a second position, and a pressure regulating piston having a pressure receiving surface which is acted on by a pressure from the second output port, and on which an elastic biasing force is exerted. Corresponding to the pressure of the second output port, the spool is moved so as to change the cross-sectional area of a flow passage that passes from the air supply port to the second output port, whereby the spool sets the pressure of the second output port to a set pressure that is smaller than the pressure of the compressed air supplied from the air supply port.